Determination of metformin in rat plasma by HILIC-MS/MS combined with Tecan automation and direct injection

Metformin is a well-known oral antihyperglycemic drug used in treatment of type II diabetes. Analysis of metformin in biological fluids is a challenge owing to its high polarity and small molecular size, which lead to poor retention of metformin on reversed-phase liquid chromatographic columns. A high-throughput method was developed and validated for the determination of metformin in rat plasma in support of preclinical toxicology studies, using hydrophilic interaction liquid chromatography tandem mass spectrometry (HILIC-MS/MS) and Tecan automated sample preparation. Extracted samples were directly injected onto the unbounded silica column with an aqueous-organic mobile phase. This HILIC-MS/MS method was validated for accuracy, precision, sensitivity, stability, matrix effect, recovery and calibration range. Acceptable intra-run and inter-run assay precision (coefficient of variation ≤ 3.9%) and accuracy (99.0-101.8%) were achieved over a linear range of 50-50,000 ng/mL. Metformin is stable in rat plasma for at least 6 h at room temperature, 147 days at -70°C and through three freeze (-70°C) and thaw cycles. Metformin is also stable in rat whole blood for at least 2 h at room temperature and in an ice-water bath. The validated method was successfully used in support of several preclinical studies where metformin is dosed together with an investigational drug substance. The ruggedness of the validated method was demonstrated by the incurred sample reproducibility test.